Embodiments of the present disclosure relate to nickel-base alloys and methods of direct aging nickel-base alloys. More specifically, certain embodiments of the present disclosure relate to methods of direct aging 718Plus® nickel-base alloy to impart improved mechanical properties, such as, but not limited to, tensile strength, yield strength, low cycle fatigue life, fatigue crack growth, and creep and rupture life to the alloys. Other embodiments of the present disclosure relate to direct aged 718Plus® nickel-base alloy, and articles of manufacture made therefrom, having improved mechanical properties, such as, but not limited to, tensile strength, yield strength, low cycle fatigue life, fatigue crack growth, and creep and rupture life.
The improved performance of the gas turbine engine over the years has been paced by improvements in the elevated temperature mechanical properties of nickel-base superalloys. These alloys are the materials of choice for most of the components of gas turbine engines exposed to the hottest operating temperatures. Components of gas turbine engines such as, for example, disks, blades, fasteners, cases, and shafts are typically fabricated from nickel-base superalloys and are required to sustain high stresses at very high temperatures for extended periods of time.
Alloy 718 is one of the most widely used nickel-base superalloys, and is described generally in U.S. Pat. No. 3,046,108, the specification of which is specifically incorporated by reference herein.
The extensive use of alloy 718 stems from several unique features of the alloy. For example, alloy 718 has high strength and favorable stress-rupture properties up to about 689° C. (1200° F.). Additionally, alloy 718 has favorable processing characteristics, such as castability and hot-workability, as well as good weldability. These favorable characteristics permit the easy fabrication and, when necessary, repair of components made from alloy 718. However, at temperatures higher than 689° C. (1200° F.), mechanical properties of alloy 718 deteriorate rapidly. Therefore the use of alloy 718 has been limited to applications below about 689° C. (1200° F.).
Other superalloys have been developed, for example, René 41® (a registered trademark of ATI Properties, Inc.) and Waspaloy™ nickel-base alloys (a trademark of Pratt & Whitney Aircraft), both of which are available from ATI Allvac of Monroe, N.C., that have increased thermal capabilities relative to alloy 718. These alloys, however, suffer from poor workability and weldability and are more expensive than alloy 718 due, in part, to the incorporation of higher levels of expensive alloying elements.
The nickel-base superalloy 718Plus® (a trademark of ATI Properties, Inc.) is generally described in U.S. Pat. No. 6,730,264, the specification of which is specifically incorporated by reference herein. Alloy 718Plus® comprises, in weight percent, up to about 0.1% carbon, from about 12% to about 20% chromium, up to about 4% molybdenum, up to about 6% tungsten, from about 5% to about 12% cobalt, up to about 14% iron, from about 4% to about 8% niobium, from about 0.6% to about 2.6% aluminum, from about 0.4% to about 1.4% titanium, from about 0.003% to about 0.03% phosphorus, from about 0.003% to about 0.015% boron, and nickel; wherein the sum of the weight percent of molybdenum and the weight percent of tungsten is at least about 2% and not more than about 8%, and wherein the sum of atomic percent aluminum and atomic percent titanium is from about 2% to about 6%, the ratio of atomic percent aluminum to atomic percent titanium is at least about 1.5, and the sum of atomic percent aluminum and atomic percent titanium divided by atomic percent niobium is from about 0.8 to about 1.3. Alloy 718Plus® exhibits improved high temperature mechanical properties compared to alloy 718. In addition, alloy 718Plus® generally has better hot workability and weldability, and is less expensive than René 41® alloy and Waspaloy™ nickel-base alloys.
In co-pending U.S. patent application Ser. No. 10/678,933, the specification of which is specifically incorporated in its entirety by reference herein, the inventors describe nickel-base alloys and methods of processing the same using solution treatment and aging. Alloys processed according to the methods disclosed therein have favorable high temperature mechanical properties, which remain substantially stable when exposed to high temperature.
Nevertheless, it would be advantageous to provide nickel-base alloys having further improved high temperature mechanical properties, while not requiring a solution treatment step during processing. As discussed in detail below, the inventors have identified methods of processing nickel-base alloys which provide enhanced, thermally stabile capabilities without the necessity of a solution treatment step.